1. Field of the Invention
This invention relates generally to semiconductor device manufacture, and more particularly, to a method of achieving very small feature size of such a device.
2. Discussion of the Related Art
FIGS. 1-3 illustrate a conventional method for forming a feature, for example, a gate, of a MOSFET transistor. As shown (FIG. 1), a semiconductor, for example silicon, substrate 20 is provided. A thin oxide layer 22 is grown on the substrate 20, and a layer of polysilicon 24 is deposited on the oxide layer 22. A layer of photoresist 26 is then provided on and in contact with the polysilicon layer 24. Using well-known lithographic techniques, the layer of photoresist 26 is then patterned (FIG. 2) to form a photoresist body 26A on the polysilicon layer 24. Using the photoresist body 26A as a mask, the unmasked polysilicon and oxide are etched away (FIG. 3), forming gate oxide 22A on and in contact with the substrate 20 and polysilicon gate 24A on and in contact with the gate oxide 22A. The photoresist body 26A is then removed, and further processing steps are undertaken as is well known to form a transistor including gate oxide 22A and gate 24A.
In etching, the width of the gate 24A is determined by the width of the photoresist body 26A. That is, if the photoresist body 26A has a width A as shown, the width of the resulting polysilicon gate 24A subsequent to the etching step will be substantially equal to the dimension A. As is well known, there is continuing interest in scaling down features sizes in semiconductor devices. It will therefore be understood that reduction in the width, i.e., dimension A of the photoresist body 26A, is highly desirable, so that the width of the formed polysilicon gate 24A is in turn reduced.
In patterning the photoresist 26 to provide a desired small dimension A, incorporating current lithographic technology, a light source of very short (for example 193 nm) wave length is used, resulting in the capability of providing a dimension A of the photoresist body 26A as small as 32 nm. However, in attempting to reduce the dimension A of the photoresist body 26A to less than 32 nm, optical interference problems arise which severely limit the ability to achieve such reduction. This in turn of course limits the ability to reduce the corresponding feature size, i.e., dimension A of the formed gate 24A.
While the example shown and described relates to the formation of a gate of a transistor, it will be understood that this problem exists for other portions of a semiconductor device wherein photoresist is used for patterning thereof.
Therefore, what is needed is a method for overcoming the above-cited problems so that feature size in a semiconductor device can be reduced.